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BUK7908-40AIE Kelvin Source

Anonymous
Anonymous
Guru 17045 points
Other Parts Discussed in Thread: CSD87350Q5D

I know this it not a TI part (it is a Nexperia part, the datasheet can be found through Digikey) but I was wondering what the Kelvin source termianal is for; it is shown in the datasheet as connected to the source terminal but what is the point of it?

  • 0
    TI__Expert 6755 points
    Andy,

    Kelvin source connections are usually used on power MOSFET devices to improve and simplify the gate drive, by having a kelvin source you take the gate drive signal out of the main switching current path and as such improve the speed and integrity of the gate drive.
    An example where we have used this at TI is with the CSD87350Q5D , this part has a kelvin source connection for the high side FET to improve switching speed and device performance.

    Chris....
  • Anonymous
    0 Anonymous in reply to Chris Bull
    Guru 17045 points
    Is the Kelvin source isolated from the regular source? As in if I was to use the BUK7908-40AIE for a high side switch (it has a current sense output) for a current mode PWM buck SMPS and didn't want the waste of a current sense resistor with the higher voltage then drain drive could the Kelvin source be safely connected to ground i.e. is it anything more then the return path for the gate. Note: the above application is just an example and is not what I am really using it for, it is something derived from an example circuit in a switching controller datasheet, so I don't need support for it if there are any errors in it is just an example. My actual application is with in a linear regulator so I wasn't sure if the Kelvin source would be of any particular use as different from the main source and if so what to do with it--the application is for a MIC5156 linear regulator as a LDO regulator.
  • 0 in reply to Anonymous
    TI__Expert 6755 points
    Andy,

    Great question.

    The kelvin source is normally only used to carry the gate drive current, as such the kelvin source wire is connected to the FET source (not isolated form the regular source as you put it) and the wire is normally only sized to handle the gate drive current and can not be used to carry large amounts of power/current. As to what specifically the composition of this device is I do not know , this you would need to contact Nexperia to get details.

    One other thing to point out, it seems your application is a linear regulator and as I am sure you know this is not a switching application, as such the kelvin sense would bring no benefit to the application. In this case it would be best to simply no connect the kelvin sense as you do not want this to be a high current/power path in your circuit.

    Best Regards
    Chris...
  • Anonymous
    0 Anonymous in reply to Chris Bull
    Guru 17045 points
    So then for a floating gate drive for the above example application would you connect the return to the kelvin source but then for a non-floating and high side application just leave the Kelvin source floating as would be the same for the linear application?
  • 0 in reply to Anonymous
    TI__Expert 6755 points
    Andy,

    The kelvin source is only designed for applications with high di/dt such as switching applications. As this is a linear application the kelvin source does not need to be used. Regardless of floating or non floating gate drive , this makes no difference.
    You could leave the kelvin source as a no connect , or, if you want, potentially tie the kelvin and main source connections together. You can tie the kelvin source to main source as the kelvin source is much higher resistance vs the main source, so current will flow through the main source. As said before you would need to contact Nexperia to understand the exact construction on their device to make sure my assumptions (that the kelvin source is much higher resistance, lower current handling source) stated here are correct.

    Best Regards
    Chris